Tweeting from his hotel room in the pre-dawn hours on Tuesday, Trump sought to heighten the suspense.

And South Korean President Moon Jae-in, who has met twice with Kim and three times with Trump, has reportedly lobbied for a trilateral meeting in Singapore to discuss a formal end to the Korean War.

HU: Now what different and unique really means, we don't know.

After the men shook hands, they repaired inside for one-on-one talks.

Word of the private tete-a-tete unleashes a torrent of criticism from national security veterans who say having aides present in high-stakes meetings provides protection and ensures no one can misrepresent what transpired.

Later in the day, advisers joined the talks for a larger bilateral session and a working lunch.

In Rodong Sinmun, the official newspaper of Kim Jong-un's Central Committee of the Worker's Party of Korea, the lead editorial strikes a conciliatory tone. It's aimed at settling a standoff over Pyongyang's nuclear arsenal.

It was a striking about-face from less than a year ago, when Trump was threatening "fire and fury" against Kim, who in turn scorned the American president as a "mentally deranged USA dotard".

The Swiss-educated leader, who is believed to be 34, has not left his isolated country since taking office in 2011, apart from visiting China and the South Korean side of the border Demilitarised Zone, which separates the two Koreas.

That hasn't stopped Trump from heightening anticipation for the summit, which he views as a landmark event that his predecessors could never have accomplished.

Trump and Kim arrived not long ago on Singapore's Sentosa Island, the site of their unprecedented summit.

While Trump and Kim shake hands, searching each other's eyes and words for signs of trust or deceit, the rest of the world will be watching, hoping that somehow these two unpredictable leaders can find a way to defuse one of the planet's most risky flashpoints. At the same time, he'd admitted he doesn't believe he requires extensive preparation to take stock of Kim. When Kim meets Trump, this will no doubt be on his mind.

Trump's early exit will be his second from a summit in just a few days. He had earlier been scheduled to leave on Wednesday. But on the eve of the summit, the White House unexpectedly announced Trump would depart Singapore by Tuesday evening, raising questions about whether his aspirations for an ambitious outcome had been scaled back. Before he leaves he'll sit for an interview with his friend, the Fox host Sean Hannity, and convene a media availability for other reporters.

We can not afford to allow North Korea, despite sanctions, to continue the development of its missile program at unprecedented speeds in the way that Iran was permitted to do so. Among the country's biggest fears is that Trump could accept a limited agreement that addresses North Korea's nuclear weapons and intercontinental ballistic missiles, but, in exchange, reduces the American military presence in East Asia.

Hannity, one of the president's most ardent supporters, will talk to Trump at the Capella Hotel on Sentosa Island in Singapore.

During this warming of relations between the two Koreas, March saw Mr Trump stun the world by accepting an invitation to meet Mr Kim.